The present invention relates to earth boring drill bits. Specifically, this invention relates to a method of producing/manufacturing earth boring bits with integral carbide studs for downhole drilling through rock and other material.
Rotary drill bits used in earth drilling are generally comprised of a cast, forged or machined material of significant hardness, to keep wear to the drill bit head to a minimum. To further enhance the effect of the drill, drill bit heads often utilize a plurality of hardened studs of tungsten carbide or other hard material mounted in a configuration on the head of the drill bit to increase the durability and efficiency of the bit. Conventionally, these studs are mounted in their seats upon the head of the drill bit by brazing or cementing them to the drill bit, which is economically inefficient, time consuming, and often results in the loss of studs during vigorous drilling. Furthermore, it is often necessary for the bits to be heavily machined after casting or forging prior to the attachment thereto of any carbide studs, requiring additional labor and costs.
U.S. Pat. No. 4,607,712 to inventor Larsson teaches a rock drill bit with studded inserts positioned within drilled holes, following the casting of the drill bit. This additional step of requiring the bit to be machined prior to the attachment of the studs requires significant amounts of resources and time.
U.S. Pat. No. 4,181,187 to inventor Lumen, teaches a method of attaching inserts to a rock drill bit using a press to force the hardened metal inserts into pre-bored holes in the rock drill bit head. Exemplifying the obstacle of extra tooling of the drill bit head following the casting, the present invention overcomes this by providing a cast drill bit head with hardened stud inserts already attached to the drill bit head during the casting process.
U.S. Pat. No. 4,499,795 to inventor Radtke teaches another method of drill bit manufacture wherein soft iron or steel plugs are embodied in the mold. After casting, the plugs are subsequently drilled out and cutting studs are inserted in their place. This extra machining significantly increases production time and cost to the drill bit.
U.S. Pat. No. 4,014,395 to inventor Pearson discloses a rock drill bit assembly wherein the hardened drill inserts are maintained in pre-drilled apertures in the head of the drill bit by tapered sleeves that are pressed into place around the studs. The addition of the sleeves increases production costs as well as the possibility of the incidental release of the studded insert due to the vibrations caused by the earth drilling process.
The present invention overcomes these problems, by providing a method of manufacturing a downhole drill bit with pre-cast carbide studs, creating a time and cost efficient alternative to the traditional methods of manufacturing requiring post-casting attachment of the carbide studs, followed by subsequent machining prior to use of the drill bit.
It is therefore an object of the present invention to provide for a downhole drill bit for earth boring, implementing a plurality of hardened carbide studs in the drill bit head which can be manufactured easily and economically.
A more specific object of the present invention is to provide a means for manufacturing a downhole drill bit for earth boring from Austempered ductile iron, or iron hardened by other means, utilizing a lost-foam casting process.
It is a further object of the present invention to provide for a means of casting a downhole drill bit head so as to attach a plurality of hardened carbide studs to the head of the drill bit during the casting process.
It is a more specific object of the present invention to provide a copper plating to the carbide studs prior to being set into the foam tooling thereby protecting the carbide itself during the subsequent Austemper heat treatment process.
It is another object of the present invention to embody a plurality of steel water tubes set into the foam tooling providing for appropriate flow of cooling liquid to the drill bit head without the need for post-casting machining of these passageways.
The foregoing objects are accomplished in the preferred embodiment of the present invention by providing a downhole drill bit implementing hardened carbide studs and method of manufacturing the same. The drill bit, cast from ductile iron, is formed by the lost-foam process. This process consists of making a foam pattern, generally out of polystyrene, having the exact geometry of the desired finished metal part. After a short stabilization period, the pattern is dipped into a solution containing a suspended refractory. The refractory material coats the exterior surface of the foam, leaving a thin, heat-resistant, semi-permeable coating, that is subsequently dried. When the drying is complete, the foam is suspended in a container that is agitated while sand is poured in and around the foam pattern, filling all voids in the coated pattern. The sand provides mechanical support to the thin coating.
Molten metal, preferably ductile iron, is then poured into the mold where the molten metal subsequently vaporizes the foam and replaces its volume. The solidified metal is formed into a nearly exact replica of the pattern which is subsequently heat treaded, preferably by the Austempering process, for application.
In this specific application of the lost foam casting process, a plurality of hardened carbide studs are partially inserted into the foam tooling in a predetermined pattern that maximizes efficiency of the drill, prior to the molten metal being poured into the mold. The carbide studs are plated in copper or some other suitable material prior to being set in the foam tooling to prevent degradation of the carbide material that would otherwise result from the subsequent heat treatment process. The carbide studs can be of various shapes and sizes. The studs are xe2x80x9cblownxe2x80x9d into the foam molds and have the necessary undercut(s) to secure them into the solidified metal and expose the appropriate cutting surface.
Not only are the carbide studs more easily attached to the drill bit head by this invention in not requiring subsequent machining of the drill bit head prior to attachment thereto of the carbide studs, but also the studs are held more securely than those implemented by alternative means, and thus the drilling head and the bits last longer and are more durable for severe drilling applications.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.